Semiconductor device and manufacturing method thereof

ABSTRACT

A semiconductor device includes a semiconductor substrate, an underlying insulation layer, a conductive via and a sidewall insulation layer. The underlying insulation layer is over the semiconductor substrate. The conductive via is through the semiconductor substrate and the underlying insulation layer. The sidewall insulation layer is between the semiconductor substrate and the conductive via. The sidewall insulation layer includes a protrusion stopping at an interface between the semiconductor substrate and the underlying insulation layer, and protruding outwardly into the semiconductor substrate.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of Application No. 15/259,992, filedon Sep. 8, 2016, now allowed, which is hereby incorporated by referencein its entirety.

BACKGROUND

Through silicon via (TSV) is one of the techniques for implementingthree-dimensional (3D) package structure. For high-density packageapplication, the dimension of TSV has shrank to micron or sub-micronlevel, and the aspect ratio of the through via is accordingly increased.The high aspect ratio of via hole, however, deteriorates step coverageof a sidewall insulation layer, thereby causing copper out-diffusingissue.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various structures are not drawn to scale. In fact, the dimensions ofthe various structures may be arbitrarily increased or reduced forclarity of discussion.

FIG. 1 is a flow chart illustrating a method for manufacturing a throughvia structure of a semiconductor device according to various aspects ofthe present disclosure.

FIGS. 2A, 2B, 2C, 2D, 2E and 2F are cross-sectional views at one ofvarious operations of manufacturing a through via structure of asemiconductor device according to one or more embodiments of the presentdisclosure.

FIG. 3 is an enlarged diagram schematically illustrating a notch inaccordance with one or more embodiments of the present disclosure.

FIGS. 4A, 4B, 4C, 4D, 4E and 4F are cross-sectional views at one ofvarious operations of manufacturing a through via structure of asemiconductor device according to one or more embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of elements and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath”, “below”, “lower”,“above”, “upper”, “on” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

As used herein, the terms such as “first”, “second” and “third” describevarious elements, components, regions, layers and/or sections, theseelements, components, regions, layers and/or sections should not belimited by these terms. These terms may be only used to distinguish oneelement, component, region, layer or section from another. The termssuch as “first”, “second”, and “third” when used herein do not imply asequence or order unless clearly indicated by the context.

As used herein, the term “through via structure” refers to a viastructure having a via hole penetrating through at least one structurallayer, and a conductive via in the via hole to electrically interconnectother electronic devices disposed on two opposite sides of thestructural layer. In one or more embodiments, the through via structureis a through silicon via (TSV) structure in which the conductive viapenetrates through a semiconductor substrate such as a siliconsubstrate.

In the present disclosure, a notch is formed from a sidewall of a viahole, and thus a sidewall insulation layer formed subsequently is filledinto the notch, forming a protrusion with thicker thickness. The thickprotrusion is configured as an etch barrier when etching an underlyinginsulation layer, and thus enhances insulation between the semiconductorsubstrate and a conductive via formed subsequently.

FIG. 1 is a flow chart illustrating a method for manufacturing a throughvia structure of a semiconductor device according to various aspects ofthe present disclosure. The method 100 begins with operation 110 inwhich a semiconductor substrate covered with an underlying insulationlayer is provided. The method 100 continues with operation 120 in whicha via hole through the semiconductor substrate is formed to expose asidewall of the semiconductor substrate. The method 100 proceeds withoperation 130 in which the semiconductor substrate is notched from thesidewall of the semiconductor substrate to form a notch. The method 100proceeds with operation 140 in which a sidewall insulation layer isformed, covering the sidewall of the semiconductor substrate andextending into the notch. The method 100 continues with operation 150 inwhich a portion of the underlying insulation layer is removed throughthe via hole. The method 100 continues with operation 160 in which aconductive via is formed in the via hole.

The method 100 is merely an example, and is not intended to limit thepresent disclosure beyond what is explicitly recited in the claims.Additional operations can be provided before, during, and after themethod 100, and some operations described can be replaced, eliminated,or moved around for additional embodiments of the method.

FIGS. 2A, 2B, 2C, 2D, 2E and 2F are cross-sectional views at one ofvarious operations of manufacturing a through via structure of asemiconductor device according to one or more embodiments of the presentdisclosure. As depicted in FIG. 2A and operation 110 in FIG. 1, asemiconductor substrate 10 covered with an underlying insulation layer20 is provided. The semiconductor substrate 10 has a first surface 101and a second surface 102 opposite to each other. The material of thesemiconductor substrate 10 may comprise elementary semiconductor such assilicon or germanium; a compound semiconductor such as silicongermanium, silicon carbide, gallium arsenic, gallium phosphide, indiumphosphide or indium arsenide; or combinations thereof. The underlyinginsulation layer 20 is formed over the first surface 101 of thesemiconductor substrate 10. In one or more embodiments, the underlyinginsulation layer 20 may include, but is not limited to, an oxide layersuch as a silicon oxide layer. In one or more embodiments, thesemiconductor substrate 10 and the underlying insulation layer 20 aresupported by a carrier substrate 30.

In one or more embodiments, an overlying insulation layer 22 is formedover the second surface 102 of the semiconductor substrate 10. Theoverlying insulation layer 22 has an opening 22H exposing a portion ofthe second surface 102 of the semiconductor substrate 10. The overlyinginsulation layer 22 is configured as a hard mask to define the locationof via hole to be formed. In one or more embodiments, the overlyinginsulation layer 22 may include, but is not limited to, an oxide layeror a nitride layer.

As depicted in FIG. 2B and operation 120 in FIG. 1, a via hole 14through the semiconductor substrate 10 is formed to expose a sidewall10S of the semiconductor substrate 10 and the underlying insulationlayer 20. In one or more embodiments, the via hole 14 is formed byetching the semiconductor substrate 10 using the overlying insulationlayer 22 as a hard mask and the underlying insulation layer 20 as anetch stop. In one or more embodiments, the via hole 14 is formed byanisotropic etching such as dry etching. In one or more embodiments, anaspect ratio of the via hole 14 is greater than 1.5, but not limitedthereto. In some embodiments, the sidewall 10S of the semiconductorsubstrate 10 is substantially straight perpendicularly or inclined withrespect to the first surface 101 of the semiconductor substrate 10. Inone or more embodiments, the shape of the via hole 14 is substantially acircular shape or a polygonal shape when view from the top. As depictedin FIG. 2B and operation 130 in FIG. 1, a bottom portion of thesemiconductor substrate 10 is notched outwardly from the sidewall 10S toform a notch 16 proximal to the interface between the semiconductorsubstrate 10 and the underlying insulation layer 20. In one or moreembodiments, the notch 16 is notched in the semiconductor substrate 10along a lateral direction substantially parallel to the first surface101 and the second surface 102 of the semiconductor substrate 10. In oneor more embodiments, the notch 16 includes a plane 16S facing the viahole 14.

In one or more embodiments, the etch rate of the semiconductor substrate10 is higher than the etch rate of the underlying insulation layer 20such that the semiconductor substrate 10 and the underlying insulationlayer 20 have distinct etch selectivity. Accordingly, the semiconductorsubstrate 10 is etched to form the notch 16 in the interface between thesemiconductor substrate 10 and the underlying insulation layer 20. Inone or more embodiments, the depth of the notch 16 is substantiallybetween 50 and 20000 angstroms, but not limited thereto. The formationof the via hole 14 and the notch 16 may be implemented in one-stage ormultiple-stage etching.

As depicted in FIG. 2C and operation 140 in FIG. 1, a sidewallinsulation layer 18 covering the sidewall 10S of the semiconductorsubstrate 10 and extending into the notch 16 is formed. The sidewallinsulation layer 18 includes a protrusion 18P proximal to the interfacebetween the semiconductor substrate 10 and the underlying insulationlayer 20, and protruding outwardly into the semiconductor substrate 10.In one or more embodiments, the thickness of the protrusion 18P issubstantially between 50 and 20000 angstroms. In one or moreembodiments, the sidewall insulation layer 18 includes, but is notlimited to, an oxide liner layer such as a silicon oxide liner layer. Inone or more embodiments, the sidewall insulation layer 18 is formed byatomic layer deposition (ALD) to fill the notch 16. In some alternativeembodiments, the sidewall insulation layer 18 may also be formed by CVD,or other suitable advanced methods. In one or more embodiments, otherstructural layers such as a barrier layer, an adhesion layer, apassivation layer or a combination thereof may be formed on the sidewall10S of the semiconductor substrate 10. As depicted in FIG. 2D, thesidewall insulation layer 18 disposed over the overlying insulationlayer 22 and on the bottom of the via hole 14 is removed by, for exampleetching to expose the underlying insulation layer 20 through the viahole 14.

As depicted in FIG. 2E and operation 140 in FIG. 1, a portion of theunderlying insulation layer 20 is removed through the via hole 14. Inone or more embodiments, the underlying insulation layer 20 is removedby etching. During etching of the underlying insulation layer 20, theprotrusion 18P in the notch 16 proximal to the interface between thesemiconductor substrate 10 and the underlying insulation layer 20 isconfigured as an etching barrier, which prevents the semiconductorsubstrate 10 from being exposed. Accordingly, after the underlyinginsulation layer 20 is etched off through the via hole 14, the sidewall10S of the semiconductor substrate 10 is still covered with andprotected by the sidewall insulation layer 18.

As depicted in FIG. 2F and operation 150 in FIG. 1, a conductive via 26is formed in the via hole 14 to form a through via structure 1 of asemiconductor device. In one or more embodiments, the overlyinginsulation layer 22 is removed. In one or more embodiments, the carriersubstrate 30 is removed. The material of the conductive via 26 mayinclude, but is not limited to, metal such as copper, tungsten, othermetals, or an alloy thereof. In one or more embodiments, the conductivevia 26 is formed by electroplating, and a seed layer 28 is formed in thevia hole 14 prior to the conductive via 26 is formed. In one or moreembodiments, the aspect ratio of the through via structure 1 is greaterthan 1.5, but not limited thereto. In one or more embodiments, thethrough via structure 1 is configured as an interposer such as a siliconinterposer in a three-dimensional package structure.

The sidewall insulation layer 18 is disposed between the semiconductorsubstrate 10 and the conductive via 26 with the protrusion 18P of thesidewall insulation layer 18 elongated into the semiconductor substrate10, and therefore a thicker insulation is formed between the conductivevia 26 and the semiconductor substrate 10. Accordingly, out-diffusion ofthe conductive via 26 is alleviated. The protrusion 18P is engaged withthe notch 16 of the via hole 14, and thus the conductive via 26 isrestricted from falling. Consequently, the reliability of the throughvia structure 1 is enhanced.

Referring to FIG. 3, FIG. 3 is an enlarged diagram schematicallyillustrating a notch in accordance with one or more embodiments of thepresent disclosure. As illustrated in FIG. 3, the sidewall 10S of thesemiconductor substrate 10 is etched to render the notch 16 have two ormore planes 16S facing the via hole 14. The sidewall insulation layer 18grows along directions L substantially perpendicular to the sidewall 10Sof the semiconductor substrate 10 and the planes 16S of the notch 16,and the multi-plane profile increases the growth rate of the sidewallinsulation layer 18 in the center region of the notch 16 than in theperipheral region. Thus, the notch 16 is able to be filled with sidewallinsulation layer 18. In one or more embodiments, the protrusion 18 is incontact with the notched semiconductor substrate 10. Accordingly, theprotrusion 18P in the notch 16 has one or more planes complementary tothe one or more planes 16S of the notch 16.

The through via structure of the semiconductor device and manufacturingmethod of the present disclosure are not limited to the above-mentionedembodiments, and may have other different embodiments. To simplify thedescription and for the convenience of comparison between each of theembodiments of the present disclosure, the identical components in eachof the following embodiments are marked with identical numerals. Formaking it easier to compare the difference between the embodiments, thefollowing description will detail the dissimilarities among differentembodiments and the identical features will not be redundantlydescribed.

FIGS. 4A, 4B, 4C, 4D, 4E and 4F are cross-sectional views at one ofvarious operations of manufacturing a through via structure of asemiconductor device according to one or more embodiments of the presentdisclosure. As depicted in FIG. 4A, a semiconductor substrate 10 coveredwith an underlying insulation layer 20 is provided. The semiconductorsubstrate 10 has a first surface 101 and a second surface 102 oppositeto each other. The material of the semiconductor substrate 10 maycomprise elementary semiconductor such as silicon or germanium; acompound semiconductor such as silicon germanium, silicon carbide,gallium arsenic, gallium phosphide, indium phosphide or indium arsenide;or combinations thereof. The underlying insulation layer 20 is formedover the first surface 101 of the semiconductor substrate 10. In one ormore embodiments, the underlying insulation layer 20 may include, but isnot limited to, an oxide layer. In one or more embodiments, an electrode12 is formed over the underlying insulation layer 20. The electrode 12may be a contact terminal of conductive wiring such as redistributionlayer, active device such as MOS transistor, passive device such ascapacitor, or other devices already formed over the semiconductorsubstrate 10. In one or more embodiments, the underlying insulationlayer 20 is an insulation layer such as a shallow trench insulator(STI), field oxide (FOX) or other insulator already formed over thesemiconductor substrate 10.

In one or more embodiments, an overlying insulation layer 22 is formedover the second surface 102 of the semiconductor substrate 10. Theoverlying insulation layer 22 has an opening 22H exposing a portion ofthe second surface 102 of the semiconductor substrate 10. The overlyinginsulation layer 22 is configured as a hard mask to define the locationof via hole to be formed. The overlying insulation layer 22 may include,but is not limited to, an oxide layer or a nitride layer.

As depicted in FIG. 4B, a via hole 14 through the semiconductorsubstrate 10 is formed to expose a sidewall 10S of the semiconductorsubstrate 10 and the underlying insulation layer 20. In one or moreembodiments, the via hole 14 is formed by etching the semiconductorsubstrate 10 using the overlying insulation layer 22 as a hard mask andthe underlying insulation layer 20 as an etch stop. In one or moreembodiments, the via hole 14 is formed by anisotropic etching such asdry etching. The semiconductor substrate 10 is notched outwardly fromthe sidewall 10S to form a notch 16 proximal to the interface betweenthe semiconductor substrate 10 and the underlying insulation layer 20.In one or more embodiments, the notch 16 is notched in the semiconductorsubstrate 10 along a lateral direction substantially parallel to thefirst surface 101 and the second surface 102 of the semiconductorsubstrate 10. In one or more embodiments, the notch 16 includes one ormore planes 16S facing the via hole 14.

In one or more embodiments, the etch rate of the semiconductor substrate10 is higher than the etch rate of the underlying insulation layer 20such that the semiconductor substrate 10 and the underlying insulationlayer 20 have distinct etch selectivity. Accordingly, the semiconductorsubstrate 10 is etched to form the notch 16 in the interface between thesemiconductor substrate 10 and the underlying insulation layer 20. Inone or more embodiments, the depth of the notch 16 is substantiallybetween 50 and 20000 angstroms, but not limited thereto. The formationof the via hole 14 and the notch 16 may be implemented in one-stage ormultiple-stage etching.

As depicted in FIG. 4C, a sidewall insulation layer 18 covering thesidewall 10S of the semiconductor substrate 10 and extending into thenotch 16 is formed. The sidewall insulation layer 18 includes aprotrusion 18P proximal to the interface between the semiconductorsubstrate 10 and the underlying insulation layer 20, and protrudingoutwardly into the semiconductor substrate 10. In one or moreembodiments, the thickness of the protrusion 18P is substantiallybetween 50 and 20000 angstroms. In one or more embodiments, the sidewallinsulation layer 18 includes, but is not limited to, an oxide linerlayer. In one or more embodiments, the sidewall insulation layer 18 isformed by atomic layer deposition (ALD) to fill the notch 16. In somealternative embodiments, the sidewall insulation layer 18 may also beformed by CVD, or other suitable advanced methods. In one or moreembodiments, other structural layers such as a barrier layer, anadhesion layer, a passivation layer or a combination thereof may beformed on the sidewall 10S of the semiconductor substrate 10. Asdepicted in FIG. 3D, the sidewall insulation layer 18 over the overlyinginsulation layer 22 and on the bottom of the via hole 14 is removed by,for example etching to expose the underlying insulation layer 20 throughthe via hole 14.

As depicted in FIG. 4E, a portion of the underlying insulation layer 20is removed through the via hole 14. In one or more embodiments, theunderlying insulation layer 20 is removed by etching. During etching ofthe underlying insulation layer 20, the protrusion 18P in the notch 16proximal to the interface between the semiconductor substrate 10 and theunderlying insulation layer 20 is configured to prevent thesemiconductor substrate 10 from being exposed. Accordingly, after theunderlying insulation layer 20 is etched off through the via hole 14,the sidewall 10S of the semiconductor substrate 10 is still covered withand protected by the sidewall insulation layer 18.

As depicted in FIG. 4F, a conductive via 26 is formed in the via hole 14to form a through via structure 2 of a semiconductor device. Thematerial of the conductive via 26 may include, but is not limited to,metal such as copper, tungsten, other metals, or an alloy thereof. Inone or more embodiments, the conductive via 26 is formed byelectroplating, and a seed layer 28 such as a titanium nitride layer ora tantalum nitride layer is formed in the via hole 14 prior to theconductive via 26 is formed. In one or more embodiments, the aspectratio of the through via structure 2 is greater than 1.5, but notlimited thereto. In one or more embodiments, the through via structure 2is configured to electrically connected to other electronic device(s)such as chip(s) or circuit board(s) through either one end or both endsof the conductive via 26 to implement a 3D package structure. Theprotrusion 18P of the sidewall insulation layer 18 is elongated into thesemiconductor substrate 10, and therefore a thicker insulation is formedbetween the conductive via 26 and the semiconductor substrate 10.Accordingly, out-diffusion of the conductive via 26 is alleviated. Theprotrusion 18P is engaged with the notch 16 of the via hole 14, and thusthe conductive via 26 is restricted from falling. Consequently, thereliability of the through via structure 2 is enhanced.

The through via structure of a semiconductor structure of the presentdisclosure includes a sidewall insulation layer between thesemiconductor substrate and the conductive via with a protrusion engagedwith a notch formed in the semiconductor substrate proximal to thebottom of the via hole. The protrusion of the sidewall insulation layerprovides a barrier between the conductive via and the semiconductorsubstrate, and thus out-diffusion of the conductive via alleviated.

In one exemplary aspect, a semiconductor device includes a semiconductorsubstrate, an underlying insulation layer, a conductive via and asidewall insulation layer. The underlying insulation layer is over thesemiconductor substrate. The conductive via is through the semiconductorsubstrate and the underlying insulation layer. The sidewall insulationlayer is between the semiconductor substrate and the conductive via. Thesidewall insulation layer includes a protrusion proximal to an interfacebetween the semiconductor substrate and the underlying insulation layer,and protruding away from the conductive via.

In another exemplary aspect, a semiconductor device includes asemiconductor substrate, an underlying insulation layer, a conductivevia and a sidewall insulation layer. The semiconductor substrate has afirst surface and a second surface opposite to each other, and asidewall. The semiconductor substrate is notched from the sidewall. Theunderlying insulation layer is over the first surface of thesemiconductor substrate. The conductive via is through the semiconductorsubstrate and the underlying insulation layer. The sidewall insulationlayer is between the semiconductor substrate and the conductive via. Thesidewall insulation layer includes a protrusion proximal to an interfacebetween the semiconductor substrate and the underlying insulation layer,and in contact with the notched semiconductor substrate.

In yet another aspect, a method for manufacturing a semiconductor deviceincludes providing a semiconductor substrate covered with an underlyinginsulation layer, forming a via hole through the semiconductor substrateto expose a sidewall of the semiconductor substrate, and notching thesidewall of the semiconductor substrate to form a notch. The methodfurther includes forming a sidewall insulation layer covering thesidewall of the semiconductor substrate and extending into the notch,removing a portion of the underlying insulation layer through the viahole, and forming a conductive via in the via hole.

The foregoing outlines structures of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A semiconductor device, comprising: asemiconductor substrate; an underlying insulation layer over thesemiconductor substrate; a conductive via through the semiconductorsubstrate and the underlying insulation layer; and a sidewall insulationlayer between the semiconductor substrate and the conductive via,wherein the sidewall insulation layer includes a protrusion stopping atan interface between the semiconductor substrate and the underlyinginsulation layer, and protruding away from the conductive via.
 2. Thesemiconductor device of claim 1, wherein the sidewall insulation layerexposes the underlying insulation layer.
 3. The semiconductor device ofclaim 1, wherein a thickness of the protrusion is substantially between50 and 20000 angstroms.
 4. The semiconductor device of claim 1, whereinthe sidewall insulation layer comprises an oxide liner layer.
 5. Thesemiconductor device of claim 1, wherein an aspect ratio of the throughvia is greater than 1.5.
 6. The semiconductor device of claim 1, furthercomprising an electrode over the underlying insulation layer andelectrically connected to the conductive via.
 7. The semiconductordevice of claim 1, further comprising an overlying insulation layer overthe second surface of the semiconductor substrate, wherein theconductive via is through the overlying insulation layer.
 8. Asemiconductor device, comprising: a semiconductor substrate having afirst surface and a second surface opposite to each other, and asidewall; an underlying insulation layer over the first surface of thesemiconductor substrate; a conductive via through the semiconductorsubstrate and the underlying insulation layer; and a sidewall insulationlayer between the semiconductor substrate and the conductive via,wherein a thickness of the sidewall insulation layer adjacent to thefirst surface of the semiconductor substrate and measured along adirection substantially parallel to the first surface is greater than athickness of the sidewall insulation layer adjacent to the secondsurface and measured along the direction.
 9. The semiconductor device ofclaim 8, wherein the sidewall insulation layer exposes the underlyinginsulation layer.
 10. The semiconductor device of claim 8, wherein thesidewall insulation layer adjacent to the first surface of thesemiconductor substrate includes one or more planes.
 11. Thesemiconductor device of claim 8, wherein the thickness of the sidewallinsulation layer adjacent to the first surface of the semiconductorsubstrate is substantially between 50 and 20000 angstroms.
 12. Thesemiconductor device of claim 8, wherein the sidewall insulation layercomprises an oxide liner layer.
 13. The semiconductor device of claim 8,further comprising an electrode over the underlying insulation layer andelectrically connected to the conductive via.
 14. The semiconductordevice of claim 8, further comprising a seed layer between the sidewallinsulation layer and the conductive via.
 15. The semiconductor device ofclaim 8, further comprising an overlying insulation layer over thesecond surface of the semiconductor substrate, wherein the conductivevia is through the overlying insulation layer.
 16. A method formanufacturing a semiconductor device, comprising: providing asemiconductor substrate covered with an underlying insulation layer;form a via hole through the semiconductor substrate to expose a sidewallof the semiconductor substrate; notching the sidewall of thesemiconductor substrate to form a notch; forming a sidewall insulationlayer covering the sidewall of the semiconductor substrate and extendinginto the notch; removing a portion of the underlying insulation layerthrough the via hole; and forming a conductive via in the via hole. 17.The method of claim 16, further comprising forming an overlyinginsulation layer having an opening over the semiconductor substrate, andetching the semiconductor substrate through the opening of the overlyinginsulation layer to form the via hole.
 18. The method of claim 16,wherein the sidewall insulation layer is formed by atomic layerdeposition (ALD).
 19. The method of claim 16, wherein the notch isformed by etching.
 20. The method of claim 19, wherein an etch rate ofthe semiconductor substrate is higher than an etch rate of theunderlying insulation layer.